1. Field of the Invention
This invention relates to a method for manufacturing a semiconductor device and, more particularly, to a method for fixing a light transmission window to a semiconductor chip incorporating a light receiving element.
2. Description of the Related Art
FIG. 6 shows the structure of a typical example of a type of semiconductor device which has a semiconductor chip incorporating a light receiving element. A lower surface 2b of a semiconductor chip 2 which constitutes an integrated circuit is mounted on a die pad 11 of a lead frame 1. A light receiving element 21 is embedded in an upper surface 2a of the semiconductor chip 2 at the center thereof in such a manner that its upper surface is exposed. A peripheral wall 3 is formed on the upper surface 2a of the semiconductor chip 2 surrounding the outer periphery of the light receiving element 21. A light transmission window 4 is placed on the peripheral wall 3 in order to protect the light receiving element 21. The light transmission window 4 may have predetermined spectral characteristics depending upon the purpose of the semiconductor device. A plurality of bonding pads 5 are formed along the periphery of the upper surface 2a of the semiconductor chip 2. The bonding pads 5 are connected electrically to inner lead portions of corresponding leads 12 of the lead frame 1 by means of bonding wires 6. The semiconductor chip 2, the peripheral wall 3, side portions of the light transmission window 4, the bonding wires 6, the die pad 11 of the lead frame 1 and the inner lead portions of the leads 12 are molded with a resin 7 while an upper surface 4a of the light transmission window 4 is exposed.
This semiconductor device is manufactured as described below. First, the peripheral wall 3 is formed on the upper surface 2a of the semiconductor chip 2 from a silicone or the like between the central light receiving element 21 and the plurality of outer-peripheral bonding pads 5 encircling the light receiving element 21. The light transmission window 4 is placed on the peripheral wall 3 so that an enclosed space 8 is formed between a lower surface 4b of the light transmission window 4 and the upper surface 2a of the semiconductor chip 2. The enclosed space 8 is provided in order to prevent the resin from entering the gap between the light receiving element 21 and the light transmission window 4 during molding and to prevent the semiconductor chip 2 and/or the light transmission window 4 from warping owing to the difference between thermal expansion coefficients of these components when the semiconductor device receives a thermal shock.
After die bonding of the lower surface 2b of the semiconductor chip 2 to the die pads 11 of the lead frame 1, the bonding pads 5 formed in the upper surface 2a of the semiconductor chip 2 and the inner lead portions of the corresponding leads 12 of the lead frame 1 are electrically connected to each other with the bonding wires 6. Then, the lead frame 1 is set in a die (not shown) and the resin 7 is injected into this die, thereby resin-molding the semiconductor chip 2, the peripheral wall 3, side portions of the light transmission window 4, the bonding wires 6, the die pad 11 of the lead frame 1 and the inner lead portions of the leads 12 so that only the upper surface 4a of the light transmission window 4 and outer lead portions of the leads 12 are exposed.
In the thus-manufactured semiconductor device, external light introduced to the exposed surface 4a of the light transmission window 4 passes through the light transmission window 4 and reaches the light receiving element 21 where the light is converted into electricity.
In the conventional semiconductor device, however, there is a risk that the position of the light transmission window 4 may shift under the pressure at which the resin 7 is injected into the die or a risk that the resin 7 will enter the enclosed space 8 during molding, because the resin molding is performed while the light transmission window 4 is in place on the peripheral wall 3, as described above. For this reason, it is necessary to perform resin molding while pressing the light transmission window 4 against the peripheral wall 3. It is also necessary that the pressure at which the resin 7 is injected be controlled in relation to the force with which the light transmission window 4 is pressed against the peripheral wall 3. Thus, there are complicated manufacturing conditions of relating the molding. It is therefore difficult to manufacture the semiconductor device with high accuracy and the desired stability.